1. Field of the Invention
The present invention relates generally to internal combustion engines for automotive vehicles and, more particularly, to a method of averaging coolant temperature for an internal combustion engine in an automotive vehicle.
2. Description of the Related Art
Today in automotive vehicles, some automotive vehicle manufacturers use "port-injected" internal combustion engines in their vehicles. In the port-injected engine, a fuel injector sprays fuel into air in an intake manifold of the engine near an intake valve of a cylinder of the engine as the air gets pulled into the cylinder during the cylinder's intake stroke. A problem with fuel delivery in all engines is that some of the fuel remains suspended in charge air or adheres to walls of the intake manifold (i.e., "wall wetting"). The amount of fuel that ends up adhering to the manifold walls is partly a function of engine rotational speed, manifold pressure, and manifold wall temperature. The amount of fuel on the manifold walls changes as the engine operational mode changes which, in turn, causes a fuel/air ratio of the charge mixture to vary as it is inducted into the cylinder of the engine.
For optimal engine performance, it is necessary for the fuel control system to compensate for this variation in the fuel/air ratio (e.g., deliver less fuel when fuel is being liberated from the manifold walls and vice versa). This compensation is accomplished by monitoring parameters that affect how much fuel will be added to or liberated from the manifold walls and adjusting a pulsewidth of the fuel injector accordingly. Whereas engine rotational speed and manifold pressure are both easy to sense and calculate, manifold wall temperature is not easy to sense and calculate because there is no sensor measuring its temperature.
One attempt to deduce the manifold wall temperature was based on engine coolant temperature which provided a coarse approximation. This coarse approximation had some drawbacks that prevented accurate fuel control during a warm-up period of the engine. The first drawback was that the engine coolant tended to warm up more rapidly than the material of the intake manifold. The second drawback occurred when a thermostat opened allowing the engine coolant temperature to "dip" with the in-rush of cold engine coolant.